1. Field of the Invention
The present invention relates to a termite detection apparatus that detects termite activity in a building and issues an alarm to the outside, and a termite alarm unit that employs this termite detection apparatus.
2. Description of the Related Art
Conventionally, an investigation as to whether or not a house is infested with termites is performed through visual inspection by an inspector who crawls under the floor at the request of a home owner. In addition, since such an investigation is normally requested by the home owner after termites have been discovered at a portion of the house that has already been damaged, by the time the actual investigation for termites occurs, damage by termites will have been in progress for a considerable time.
To deal with the problem discussed above, the applicant of the present invention disclosed a termite alarm unit in Patent Application No. H6-170134 dated Jun. 29, 1994 (Japanese Unexamined Patent Publication No. H8-9860). The termite alarm unit disclosed in this application comprises a sensor section constituted with a cellulose containing member that is provided with a plurality of through holes extending transversely, each hole having one opening end provided with an emitting element and the other opening end provided with a receiving element, a judgment section for detecting an infestation of termites to provide an output signal in response to the obstruction of an output wave from the emitting element to be received by the corresponding receiving element and an alarm display section for issuing an alarm in response to output from the judgment section.
Also, Japanese Unexamined Patent Publication No. H6-205632 (Declaration of Priority No. 941460, priority date: Sep. 8, 1992, Declaration of Priority filed in: USA) discloses a unit that monitors for termite activity, determines the degree of infestation and arrests the infestation when termite activity is detected. The unit disclosed in this publication comprises an external housing 2, which is permanently buried underground at a specific depth, and a cartridge 12 provided inside the housing in such a manner that it can be removed, with a hole 4 formed in the external housing 2 and a hole 14 formed in the cartridge 12 positioned so as to become aligned with each other when the cartridge 12 is mounted inside the external housing 2. In addition, this publication discloses that initially, the cartridge 12 containing a non-toxic bait material, is mounted inside the external housing 2 in order to diagnose the level of the infestation of termites and is regularly taken out to check for termite activity and that when termite activity is detected, the cartridge 12 mounted inside the external housing 2 is charged with a toxic bait material instead of the non-toxic bait material in order to prevent the infestation from spreading.
The unit disclosed in Japanese Unexamined Patent Publication No. H7-23684, which detects an infestation of termites in a house at an early stage and enables prompt countermeasures to be taken by sending the results of the detection to the manager of a center via a telephone line, comprises a detection terminal 2 and a detection sample 1 to which the detection terminal 2 applies a specific level of pressure. When the detection sample 1 begins to disintegrate from being eaten away by termites, the displacement of the detection terminal 2, which occurs as the detection terminal 2 caves in toward the detection sample 1, is detected. In particular, the displacement of the detection terminal 2 is detected by a magnetic sensor 7.
The invention disclosed in Japanese Unexamined Patent Publication No. H7-115887, which was filed by the same applicant as that of the invention disclosed in the Japanese Unexamined Patent Publication No. H7-23684 described above, is characterized, in addition to the basic structure disclosed in Japanese Unexamined Patent Publication No. H7-23684, by the following: a gap provided in the fitting area between the woody portion for detection and the case; the woody portion for detection is in the form of a plate with pressure applied in a direction that is at a right angle to the cross grain surface; pheromones employed as the attractant for termites; and in particular, in regard to the magnetic sensor: a 52 alloy or the like, with a high magnetic permeability and low level of residual magnetism is employed for the metal plate which constitutes the magnetic circuit and a structure for shielding magnetism provided at the external circumference of the magnetic circuit.
Japanese Unexamined Patent Publication No. H7-255344 discloses a unit which detect vibrations that occur when termites eat a substance such as a piece of wood for detection. This unit is provided with, in the sensor main body, a means for placing a substance that constitutes a desired food for termites near the path of infestation of termites and a means for detecting vibrations that occur when the termites eat the substance or the vibrations that occur as a result of termite activity. To be more specific, the termite sensor disclosed in this publication comprises a sensor external frame; a battery to function as a power source; a vibration sensor for detecting vibrations; a signal processing circuit for amplifying and processing signals sent from the vibration sensor; a lever that communicates vibrations to the vibration sensor; woody material as bait for termites; a spring for holding the woody material in contact with the lever; a bait table and a sensor bottom portion.
In addition to the structural features disclosed in Japanese Unexamined Patent Publication No. H7-23684 described above, the unit disclosed in Japanese Unexamined Patent Publication No. H7-274792 is further provided with a means for supplying moisture to the woody material which is used as a detection sample, in order to increase the effectiveness of detection by taking advantage of the termites' affinity for moist wood.
A termite detection apparatus disclosed in Japanese Unexamined Patent Publication No. H7-143837 comprises two acoustic sensors which convert the sound of termite activity to electrical signals, a subtraction processing device which performs subtraction processing for signals provided by these acoustic sensors and a comparator which outputs signals upon which the subtraction processing has been performed and which are at a level higher than a specific threshold value, as termite detection signals, in order to enable accurate detection of termites without being affected by noise from the outside.